Geometric morphometrics of adolescent idiopathic scoliosis: a prospective observational study

Adolescent idiopathic scoliosis is the most prevalent type of scoliosis, and its consequences on the human torso have not been deeply studied. In spite of being a 3D condition, clinical management is circumscribed to 2D images among health-care professionals. GMM is a well-recognized tool in the study of 3D shape and symmetry.

Twenty-four subjects with AIS and 24 controls were subjected to surface scan. Digitization and shape data were extracted and submitted to GMM analysis. 3D shape and asymmetry were correlated with Cobb angle in subjects with X-ray availability. Comparisons of mean shapes were done between each group and its symmetric average shape and between each group at two states: initial and 6 months after.

AIS and controls show similar areas of asymmetry, being significantly higher in quantity in AIS (PD = 0.045; PD 0.037; p < 0.001). Significant correlation was observed between Cobb angle and Procrustes asymmetry (r = 0.38; p = 0.01) as happened with 3D shape (r = 0.11; p < 0.001). No significant changes were observed in the 3D shape of both groups 6 months after (AIS, p = 0.51; control, p = 0.304).

The greater asymmetry observed in AIS was expectable, but the similarity of areas of asymmetry in both groups made us suspect of directional asymmetry in the human torso that could explain the high prevalence of right scoliosis observed in nature. The shape of the torso and the asymmetry should be considered as variables to study in AIS due to its correlation with Cobb angle. Progression of the deformities was not observed in our study, maybe due to short-term follow-up.